1. Field of the Invention
The present invention relates to a portable optical detection chip and a manufacturing method thereof, and more particularly, to a biochip capable of parallel scanning in a dot-to-dot manner.
2. Description of the Related Art
The merits of biochips focus on utilizing fewer specimens and promptly and simultaneously detecting a plurality of diseases or specimens. The protein structure of a protein chip, a kind of biochip, has poor resistance to environmental conditions and easily becomes dormant; hence an optical detection method that is less harmful to protein specimens is commonly utilized for biomedical research. Such optical detection types include diffraction, absorption, fluorescence and many other types of measurements so the variable values of light intensity, frequency, polarization, phase shift and so on are measurable.
FIG. 1 shows current effective detection methods and distribution ranges of their response concentration. The most advantageous of the photoelectrical technologies currently employed in the biomedical field is the fluorescence (or fluorescence spectrum) method due to its high sensitivity. In general, a fluorescence radiation rate is directly proportional to the concentration of the sample under detection. However, high concentration of the sample easily results in self-quenching and self-absorption problems in the fluorescence, and the fluorescence radiation rate is reduced. The sensing spectrum of the fluorescence method is similar to that of an absorption spectrum analysis method. But unlike an absorption spectrum analysis method, the fluorescence method needs a light source with high intensity such as a laser beam and white light because fluorescence-sensing molecules with high quantum yield are necessary and the signals to detect emitting light are easily affected by environmental factors such as temperature, pH values and ion intensity. After the fluorescence-sensing material reacts on the sample under detection, its structure, phase shift and half-life period are changed. The concentration of the detected sample is indicated by variations in these measured parameters.
Even though an electrochemistry method or a bioluminescence method can reduce interference from light sources so as to achieve the limitation pM of detected concentration, their applications are generally restricted by specificity. By contrast, the fluorescence method is less invasive to a substance with a detectable concentration below pM, and is a preferable method if it is performed with a miniaturized and highly-sensitive detector. A surface plasmon resonator can achieve nM concentration, create a label free system and perform quantative analyses, but such a resonator cannot easily fabricate portable and array chips like other methods. The fluorescence method can detect substances below pM and is non-invasive, highly sensitive, selective, able to provide multiple emissions (varying in intensity, phase, polarity, and life cycle), and is capable of minimization and arraying. A general fluorescence sensing system is primarily comprised of light sources, filters, spectroscopes, and optical detection elements with operation based on the principles of optics including spectrophotometry, optics of fluorescence and reflection, etc. This is a complicated system with a larger volume, and the optical detection elements and peripheral elements cannot be integrated with each other. Therefore, the objective of the present invention is to microminiaturize the fluorescence sensing system in order to achieve portability.
Tuan Vo-Dinh puts forth an integrated chip comprising bio-probes, samplers and detectors (including amplifiers and logic circuits). Consequentially, the feasible model of a DNA biochip detection system is obtained. Unlike other biosensor methods, Tuan Vo-Dinh's proposed method stamps or dots bio-molecules on a treated glass slide, and then the bio-molecules are detected by a system including an enormous amount of laser excitation sources and photosensors. The system comprises a great deal of elements, which negatively impacts the detection rate. The complexity of the system needs to be reduced so that the rate is prompted.
American Axon Co. puts forth a bio-scanner system with model No. GenePix 4000B. This commercial product has advantages of 5 μm resolution, double lasers, changeable focus and changeable laser power. It is a powerfully functional optical scanning system. However, the system requires a precise movable platform, an optical lens set and a detection module, so it is difficult to minimize the size of the system for portability and reduce the manufacturing cost to a level enabling disposability.
More common types of equipment currently applied in fluorescence detection include:
1. Confocal Laser Scanning Fluorescence Microscopy (CLSFM): Laser rays are condensed by a high-resolution microscope, and a sample of dots on a biochip is scanned. Photons emitted from the sample dots excited by the laser are collected by the microscope, and subsequently illuminate a highly light-sensitive phototube through a tiny pin hole. Because a point light source placed at a front focal point of the microscope is condensed at a back focus of that, except for an excitation light placed at the sample plane, nearly all scattered lights behind or ahead of the sample plane are filtered, if the front focus is aimed at the sample plane and a pin hole is located at the back focus. In this regard, it appears that the microscope has a very high vertical resolution at that time. Furthermore, if the magnification of the microscope is high, the laser rays are condensed into extremely tiny spots so that the horizontal resolution of the microscope is also excellent. Therefore, the greatest advantage of CLSFM is its very precise three-dimensional resolution capability, which can greatly enhance noise control capacity. A drawback of CLSFM is that it costs more because more time is required for chips with a large area and a greater number of sample points. A further drawback is that laser points focused by the lens have an extremely high intensity and when scanning sample points this inevitably causes damage to the sample.2. Charged-Coupled Device (CCD): The technique involves shining rays evenly over an entire chip, taking an image of a chip by a CCD camera and inputting the brightness of each sample point as determined by a computer. Because the images of all sample points are simultaneously read and charge-coupled, speed and efficiency are significantly enhanced in comparison with the CLSFM. In addition, as illumination is not focused, it is unlikely for intensity to cause damage to samples. However, there are very strict requirements on optical elements, including the illumination source, imaging system, CCD selection, multipoint CCD, and front and back optical paths when using CCD. Furthermore, the system is very large and its cost is high.
In view of above, it appears that the conventional optical detection system can be improved by implementing the MEMS (Micro Electro Mechanical System) method and miniaturizing some elements. Accordingly, the conception of Lab on Chip is implemented.